This thesis describes the synthesis and characterization of near-infrared (NIR) emissive conjugated polymers and their polymer dots (Pdots). The Pdots were exploited to image the tumor cells and tumor spheroids. The penetration behavior of NIR emissive Pdots was characterized in five different tumor spheroid models. Three different polymerization techniques were tried to synthesize the NIR emissive polymers, namely oxidative, direct arylation, and Stille polymerization. The obtained NIR emissive polymers underwent structural and optical characterization. P1 was chosen as a model polymer to obtain Pdots from NIR emissive polymers for imaging tumoroids. Pdot preparation includes using ultrasonic emulsification to modify nonionic D-A-D type alkoxy thiophene-benzobisthiadiazole-based conjugated polymers (P1) with amphiphilic cetyltrimethylammonium bromide (CTAB). The technique yields Pdots with a significant positive surface charge of +56.5 mV ± 9.5 and an average hydrodynamic radius of 12 nm. Optical characterization reveals that these Pdots were found as emissive in the NIR region, with a maximum wavelength of 860 nm. These Pdots possess colloidal and optical properties that make them appropriate for use as fluorescence emissive probes in bioimaging applications. The advantageous use of positively charged Pdots has been proven in diffusion-limited settings such as tissues, specifically in certain tumor spheroid models produced from the tumoroid cell lines. After the fluorescence imaging analysis, the Pdots' emission intensity profile indicates that they have high penetration capability into the tumoroid models' center parts. The results show that Pdots with a single-chain donor-acceptor polymer structure that has been cationized with CTAB can penetrate through dense materials over about 1 µm. This provides valuable insights into the progression of targeted theranostic strategies in cancer therapy.